Metal stretching press



y 14,1942- H. F. MacMILLlN ETAL 2,289,534

METAL STRETCHING PRESS Filed March 25, 1940 s Sheets-Sheet 1 4 3 4 5 5M 5 a m m a w flum fi z M 1 4a m I mmmm 25 l I 1 no a w 5 mm? u 1 M 9 W Y MMJW/ Q n a 4 H v I l W H v M Q July 14, 1942.

H. F. M MILLIN ETAL 2,289,584

METAL STRETCHING PRESS 3 Sheets-Sheeii 2 Filed March 25, 1940 Ira-.4

ATTOPNEYS piecetothepress.

- of these forces obviouslyrequiresa ipp eflect I worked. Obviousl drawn until contact with the metal, Moreover, in ,so-called stretching presses in which; certain slippage of permitted ands-required to accomoften diilicult to make the timing but also and it is harder yet to change the adjustments or the-clamps, individually eflfects. v A primary objector the present invention ,is to provides hydraulic press which is adaptedacter.

' -Patented July 14, 1942 assets METAL s'mnrcnmc rnass Howard F. Mac

Tucker, Dayt fi Gilead, Ohio,

Mount Gilead, Warren B. and Keller Thor-econ, Mount w assignors A Development Corp. Inc., L corporation of Delaware to The llydraulie Wilmington, DeL, a

Application- March 25, 1940, Serial No 325,780

, 9Claims The resent invention relates to hydraulic presses. and particularly to presses or the type that. employ-mechanism tor clamping the work- In certain forms of hydraulic drawing presses it is sometimes necessary t'o-clamp the sheet of metal'to the bed or ious methods for doing this havebeen proposed, and practically all of these methods depend on the use of clamping or gripping forces derived -from pneumatic cylinders, electric motors or hand-power-operated through levers. The f use source. of energy dinerent tromthat employed in the press, which adds to expense oi thepress as a whole, also to the installation and,to the com-l plexityoi' operation. Furthermore, the powermultiplying levers areoiten oi a complicated mechanical character due to the manner and direction in which the forcegis applied.

o1 e e ng pressing forces,

is provided before the metal is this timing requirement is dimcult to achieve and maintain, where separate sourcesoi' energy are employed for the gripping and pressing operations.

Another precaution-which must be taken is v to insure that the clamping eflect is not withthe 'punchoi the press has broken the metal is modatethe drawingor forming operation, it is necessary adjustments of the prior-art clamps to not only insure proper the proper amount or slippage.

tcproduce local pressing to grip the work with, or withoutslippage, and

to eliminate all oi the disadvantages in connccprior-art presses at this general char tion with Another object source; 01' power which is employed clamping effects are obtained y irect hydraulic pressure, thus insuring perfect coordination between the press and the 56 in top plate or the press. Varthis general type quite frequently between the clamping and particularlrito insure that the is :to provide a ,press in which the v81111114 8 or blank holderiaws aresacted upon by the same tor-operating thepressr i "A further object is;- to provide a hydraulic press in which the work-clamping mechanism. Only a single source of hydraulic powergis required for these two purprices, so that when pressure is applied to the: fluid otthe press the clamping mechanism is simultaneously subjected to the pressureof the v A still further-object is to provide a hydraulic press in which the workpiece is gripped at a number or diiierent areas throughout the surface of theworkpiece, and ready adjustment may .be made or the final clamping eil'ects at the various clamping positions.

.In carrying out the above objects there is pro-' ided a number or hydraulically actuated pistons for applying pressure to a'similar number of clamps or gripping devices spaced about the wor piece and receiving their power from the same source or pressure fluid which operates the .iusted as a' whole or individually in order to pro- Other objects and features will be apparent as the specification is perused the accompanying drawings:

Inthedrawings: a

Figure'l is a pe p ctive view, with apart broken away and in section,

Figure 2 is a lateral section takenacross the press shown in Figure 1 and along th line 2-4 in Figure 3. but with the plunger in elevation and the hydraulic circuit shown schematically.

Figure 3 is a viewvtaken alongthe lined-4 in Figure 2, and showing the'relation between the press plunger and the cylinder in which the plunger operates.

40a Figure 4-is a fragmentary sectional view of a press similar to that shown in the preceding figurea. except employing, a difl'erent form of hydraulic circuit. ,{I'he latter is illustrated by diaram.

:isa perspective view, partly broken away, of still another modification oi the improvedpress.

\ Figure '6 is a sectional view taken along the flline 8-8 in Figure 5, eircep't that the-press and immediately, associated apparatus areshown in elevation"; Figurefii employs a diilerent form of hydraulic :circuit from that illustrated in F'igures 2 and 4. v

Referring more particularly to the press shown Figures 1, 2 and 3, the numeral l designates press. Each of these pistons. reciprocates in cylinders, the pressure 01' which may be ad-v vide the necessary general or special clamping in connection with of a hydraulic press, improved in accordance with the present invenoutwardly from ahub 01 at 31 and II.

rod 33 which is secured to I- pair-of pistons 2 in general the bed of the press. This bed is provided at the bottom with a base 2, of rectangular configuration, from which extend upwardly, preferably midway between opposite edges of the base, a number of webs 3. These webs radiate cylinder 4 integrally joined to the base. The interior of the cylinder -wall is preferably ground, and receives a piston 5 provided with the usual rings 5, the piston being carried by a plunger 1' to which is secured at the upper end a platen 3; The latter detachably carries a punch 9, having rounded edges, as indicated at it, and of a configuration determined and 4!, respectively, joined together by a rod 42.

The pistons 40 and 4| are specially related in such a way as to control the passage of the pressure fluid to and from the valve, in accordance with longitudinal movements of the rod 39 and .for purposes which will be explained presently.

This rod may be pivotally secured to any convenient form of hand or automatic operating mechanism, such as a lever systemcr the movable core of an electromagnet or a crank driven by a motor. In any of these cases the rod 39 is adapted to be moved in a horizontal direction by the shape of the article, indicated at I I, which is being pressed.

The base 2 is. provided at each comer thereof with an upstanding cylinder 12, preferably formed integral with the base, as'by'casting,

these cylinders being reenforced by the triangular webs l3. Each cylinder contains a reciprocaferent lengths of pipe 43, 44 and tory piston l4 with rings 15 and .carried by the piston rod l6, which is provided with a top threaded portion of smaller diameter than the lower or main portion, to leave a shoulder II.

A nut is provided on the threaded portion.-

The piston is provided with the usual packing material and gland, indicated generally at IS. The centrally positioned piston 5 is provided with a washer is, packing material 20 and a. packing gland 2| which can be drawn toward the cylinder 4 bythe bolts 22, thus compressing the packingmaterial. As indicated in the drawings, the.

cylinders l2 terminate at the same height, and

.on top of these cylinders there is positioned a hollow rectangular frame 23, termed the top plate, having openings through which the rods l5 extend.

Directly above thetop plate therefrom by the thickness of the metal sheet l l, and resting on the shoulders l'l', there is a gripping plate 24 having. a configuration similar to that of the top plate. The clamping nutsla bear against the upper surface of the r pp plate so that as downward pressure is applied to these nuts the plate 24 serves to clampthe metal sheet I I to the topplate 23. R As-ill'ustrated more clearly in Figures 1 and 2,- the plates'23 .and 24 constitute a frame with large rectangular openings therein which are adapted to receive the sheet metal while it is being formed to the required shape. There is a number of die strips 25 detachabl secured to 'the interior surfaces of the plates 23, 24, as for example, by means of bolts 26. These strips are preferably made of receive the bolts 25.

- For operating. the press there'is provided a 23 but I spaced at a predetermined time and for a predetermined distance, depending on the operation desired of the press.

There is a conduit, represented by three dif- 45, extending from a position at the back of "the piston 5, through the cylinder walls 4 and I2, to a position at theback of the piston l4. In the length of pipe 44 a check valve 46 is provided. This valve is of the one-way type and of any suitable and well known construction. As illustrated, the actuating element of the valve is constituted of a vane 41 pivoted at 48, the arrangement being such that fluid can pass from left to right through the pipe length 44, as indicated by the arrow, but not inthe reverse direction.

Extendingfrom the pipe section 43 there is a pipe 49 containing a check .valve 50, which is so arranged as to permit fluid to pass upwardly through the pipe (as seen in Figure 2) but not in the downward direction. The pipe 49 communicates witha horizontally positioned pipe 5i, the ends of which-terminate at the lower surface of two oppositely positioned cylinders l2, directly under the pistons M. It will be understood, since there are four cylinders l2, that there are two sets of pipes 5|, of which only one has been illustrated, with a cross connection conduit between the two pipes in order to assure the same pressure throughout the two pipes and therefore the same pressure applied to the under sides of single one-way hydraulic pump 2'1,-which may be actuated by an electric nibtor'motshown) The outlet or the inlet at :9.

pump is indicated at 24 and the The latter is connected, through a metal conduit 30, with a tank 3| containing asuitablefluid, for exampleoil; The ,outlet of the pump is connected through a metal conduit I 32 with a four-way valve 33, of any suitable and well known type. The high pressure ingress to the valve is indicated at 34 and the low pressure egress at 35. There is also a low pressure pipe II. The high pressure discharge pipes are shown The valve 23 contains a piste:

The pipes 5| are connected through a conduit 52'to the upper side of the valve 33. There is a horizontal length of pipe 53 extending from a position in backof the lefthand piston l4 which communicates with a vertical length of pipe 54, and terminates in the pipe 5].

An admission valve all of the pistons 14.

55 is inserted in the horizontal length of pipe 53. admission valve is of any suitableand .well construction and has for its purpose the passage of pressure fluid from left when ,the pressureuin the pipe is in excess of a predetermined'pressure. The valve may be constituted, as a typical form, of a cylinder 56 containing two chambers, one. of which is indicated at 51 and is of greater diameter than the'other, indicated at 58. The top of the valve is closed by a plate 59. A compression spring 6|! is positioned in the chamber of larger end of this spring bearing against a collar 6| which is carried on a piston 62. Beneath the piston there is a second piston 63 separated from the first piston by an undercut portion 54.

The valve 55 has an opening at the bottom which receives an upturned pipe 65. The arrangment. is such that when the pressure in the pipe 55 is below a predetermined pistons 62, 63 remain in the position assh owrfin Figure 2, in which the upper piston closes of! the pipe 53, thus preventing the passage of any fluid through the pipe. on the other hand vhen to right through the pipe 53.

diameter, one

cunt the e v the 'cylinder for an true with respect to the l in the casing 13 which contains a .15, and returning the a predetermined pressure.

{constitutes a pressure safety further explained hereinafter.

mined amount, the piston 63 is caused to move upwardly against the restraining action of the spring'60, and this in turn', causes the upper piston. 62 to move into the upper chamber 55,

leaving the undercut portion 34 in the pathway constituting the pipe 33. Since the diameter of this undercut portion 34 is less than the internal diameter of. the pipe 53, fluid under pressure can now pass throughv the pipe 53., The function of the admission valve 53 with respect to the remaining elements ofth e system will be explained in connection with the operation of the device as a whole. J

'There'is apipe '66 which terminates in the v I 2,289,884 the pressure in the pipe 63 exceeds a predeterfiguration. The punch 3 is first designed, either .by calculation or experiment, to produce this configuration when the plunger 1 is operated. 'The' rod 39 of the four-way valve is moved to the right, and assuming that the hydraulic pump 21 is being operated, pressure fluid will pass through gripping plate 24 to move upwardly away from pipe 53 at a position between the valve Ii and through a horizontal pipe length 61 to a vertical pipe length. 63. The latter joins with the two horizontal pipe sections 44, 45. A pipe 69 is taken from the lower interior surface of the cylinder 4, -i. e. at the lower side of the piston 5,

to the'top of the. valve 33, where it terminates in of pipe 10 terminating at the left-hand end at the cylinder l2 and positioned above the bottom of appreciable distance, the purpose of which will Ill connects with a vertical pipe H which terminates at the bottom in the low pressure pipe 30, h

While this pipe system has been described mainly in connection with only a pair of cylinders I2, it will be understood that the pipe-connections which are made to the right-hand cylinder are also made to the cylinder the right-hand cylinder, and the'same thing is pipe connections made to the left-hand cylinder. Similar pipesare provided with lateral extensions in order to as-' sure that-the same pressure prevails throughout the diiferent corresponding cylinders. Obviously,

if desired, the pipenetwork can be so designed.

as to necessitate only one admission valve 35 and only one set. of check valves 41 and ill, these valves serving to perform their special-' function corresponding pipe lines ofthe entire system.

The hydraulic pump 21 is preferably of the radial, piston' type, in which the movement of the pistons is controlled by a flow or shift ring I appear presently. The right-. hand end of the pipe the cylinder l2, this pipe 66 being connected.

the plate 23 because the shoulders II'.

As the pistons l4 continue to move upwardly,

plate 24 rests on the at least one of them will eventually uncover the opening in the pipe 13 which is connected to the low pressure pipe", and in efiect, will causethe discharge of the high pressure fluid back to I the'tank. The pistons i4 will thereupon drop I a slight amount until they cover the pipe Ill,

. and will bemaintained in this position by the pressure fluid flowing through the pipes 5|. Thus the fluid egress 35: There is a horizontal length a in 'back of the pistons l4 will float or flutter at this elevated position, holding the grippingplate 24- at a considerable height above the top plate I 23. The edges of themetai sheet H can then be readily'inserted in this deep space between the plates 23 and 24, and when properly positioned the clamping pistons are drawn downwardly by admitting pressure flui tothe upper sides of the pistons and exhaus he( fluid from the lower sides thereof.. This operationus ac.- complished by moving the rod 33 to the left in the position shown in Figure 2. It will he noted under these conditions that the pipes ii are connected directly to the tank 3|, through the pipe 32, the valve and the pipe 35. Pressure fluid is admitted through the pipe 32 into the valve 33, and through the-pipe]! to the under. side oflthemainpistonl p p This pressure fluid will cause the piston I- to elevate, but beforethe punch lhasactually. contacted-with the underside of the metal sheet H, the fluid which is trapped between the upper,

' side of the piston 3 and the washer l9v (introindicated in a fragmentary manner'by'the refpressure outlet 28 of the pump. The purpose of the casing is and the contained mechanism is to stop thedischarge of the pump by causing the piston 14 to move to the right against the spring. shift ring 12 to neutral when the pressure in the pipe I1 is higher than device, as will be erence character I2. Extending outwardly from to. the shaft ring 12. e plston bears against clamping nuts l8. As the piston 5 continues its duced through the immediately preceding operation) is placed under pressure and this pressure fluid passes through the pipe sections 43,

44 and 45 into a pair of cylinders i2 above the pistons i4, and another portion of this fluid will pass through the pipes 33, i1 and i3, into'the other pair of cylinders above their respective" pistons. The-effect of this pressure fluid: is'to cause all of the pistons i4 to move downwardly, ca rying with them the gripping plate 24, due to the compression stresses exercised at the upward movement the pressure'of the fluid in the cylinders I2 becomes greater and greater, causing increased clamping effects at the nuts 13 so that by the time the'punch actually con ment, causing a deformation of the metal-sheet to'a shape dependent on the configuration of Thus the unit 13 Operation I 7 Assume that it is desired to draw out or form the sheet of metal ll into a dish-shaped consheet are firmly-held between the plates tacts with the metal sheet all four edges of the 23 and 24'. The plunger 1 continues its upward movethe punch and theshape of the die strips 23.

In drawing operations of. this "character it is I usually desirable, but not always, to'permit a small amount of slippage between the metal sheet and the gripping plates. For this reason it is necessary that the clamping effects of the pistons I4 shall not begreater than a predetermined maximum. This desirable result is brought excess pressure fluid can the pipe 52 and the valve 33 to the tank 3|.

about in a novel manner by the use of the ad- 7 mission valve 55. As the pressure builds up at move upwardly against the spring 60 and into the chamber 51, and the undercut portion 64 will now be presented to the pipe 53. Thus the immediately pass through the pipe 53, through the valve 51, down through the pipe section 56, and exhaust through As soon as the excess pressure fluid is relieved through the admission valve 55 the piston 52 will descend to its initial position directly in line with the pipe 53, thus maintaining the pressure in the upper portions of the cylinders l2 at a predetermined value.

As the piston is continuing its work on the metal sheet H it will eventally reach its uppermost limit .of movement, and this may be determined in a number of ways. The operator,

.for example. may observe the height to which the central portion of the metal sheet has been raised by any convenient reference point or measuring device, and when satisfied that the sheet has been completely formed he may cause the rod 39 tobe moved to the right, which will cause the plunger 1 to descend, as will be explained presently. However, there is illustrated a pressure-operated means for reversing the travel of v the plunger, and this is effected through the pump 21.

Assume that the piston'has just reached its maximum upward travel and tends to go higher.

The pressure of the trapped fluid back of the piston becomes excessive, and this imparts an excessive pressure load at the pump. The resuiting excess fluid passes 'from the outlet 28, through the pipe 11, to the left-hand side of the piston 14, causing the shift ring 12 to move back to neutral againstthe action of the spring .25. Under these conditions, as is wellknown,

the output of the pump is reduced to zero, thus relieving the excess back pressure at the main piston.- When the operator has observed that the pressure safety device has operated he can immediately cause the rod 39 to be moved to the right to exhaust-the pressure fluid from the under side of the piston 5. It is obvious that if desired an automatically operating mechanical or hydraulic system may be employed for moving the rod 39 at the same time that thepiston 14 in the pressure safety device 13 is operated.

. Upon movement of the rod 39 to the right the pipe, 39 is now presented directly to the tank 3|,through the valve 33 and the pipe section 36,

thus permitting the fluid in the lower portion of I the main cylinder to be exhausted. 0n the other.

hand, pressure fluid from the pipe 32 (assuming that piston H has been moved to the left on reduction of the excess pressure, permitting the flow ring 1-2 to be shifted away from neutral by the spring l6) flows through the valve 33, into' the pipe 52. From there the pressure fluid passes upwardly through the pipe 49, the pipe. section 43, into the space at the back of the piston 5, thus causing the piston to'descend and break contact with the metal-article II. It will be noted that under these conditions the pressure shape and size.

sequently, clamping pressure is still being exercised by the piston rods 16 even after the punch 9 starts to descend. a

In addition to providing pressure fluid to the upper side of the piston 5; as explained-above, fluid is also introduced into the pipes causes the pistons M to move upwardly and to elevate the plate 24 from the plate 23. However, it will be understood that the pistons I! do not move upwardly immediately after pressure fluid is introduced into the pipes 5| because there is a greater pressure on the opposite sides of the pistons urging the pistons downwardly. due to the pressure sett'ng of the valve '55. Thusthe clamps remain set until the punch 9 has descended an appreciable distance, or at least until it has become stripped from the metal article, at which time the pressure built up at the under side of the piston is greater than the back pressure at the upper side of each piston. As the-plunger continues to despend the pistons M will continue to rise their uppermost elevated position, determined by the level of the pipes 10. The article ll may be then readily maneuvered out of position between the plates 23 and 24, notwithstanding the fact that the edges of the formed article extend under the die strips 25. It is obvious that the amount is disclosed an improvedform of hydraulic pressin which the clamps are actuated from the same source of hydraulic energy as operates the main press. tomatic inits operation since the same valveas controls pressure fluid to the main press, and further that the arrangementkis such that the clamping effect is made effective at a time prior to actual contact between the punch and the metal sheet during the upward movement of the plunger, and is maintained at its proper value for a predetermined length of time after the punch has stripped itself from the finished article. It is also apparent that a very careful adjustment may be obtained through the valvef55 to provide not only the'clampinglefiects necessary to hold the metal sheet ll without slippage, but also to provide a predetermined amount of slippage in order to facilitate the drawing or stretchmg of the metal.

The use of the rectangular gripping plate 24 it is controlled by permits a fabrication of all kinds of complicated shapes of the metal article, since the metal sheet 24 may assume any other shape than rectangular, such as circular or elliptical, or indeed may constitute simply a pair of heavy strips or bars so as to hold only .two edges'of the metal sheet. Changes in the configuration of the metal article may be readily accommodated by simply replacing the die strips 25 by other strips of suitable It will be further noted that, due to the manner in' which the spaces at the upper sides of the pistons M are all connected together through the common conduit 44 leaduntil they reach The clamping mechanism is entirely authe transmission of" ing from the upper side 01' the main piston 5, the pressures causing .the pistons II to move into clamping position are all equal. This results in an equal distribution of the compression stresses exercised throughout the plate 24 on the metal sheet H.

- In Figure 4 a modified form of hydraulic circuit is" shown. Whereas in the circuit illustrated in Figure 2 the clamping pressure appl ed to the- T rear of the pistons i4 is obtained from the compression effects atthe rear of the main piston 5, in Figure 4 these clamping eflects are obtained directly from the pump. Moreover, in Fi ure 4 a pipe is taken from the rear side of the clamping pistons It to the under or working side of the piston 5, with a pressure limit valve placed in this pipe so as to assure that the'main piston will not elevate until a predetermined pressure has been built-up in the clamping cylinders.

Referring in detail to Figure 4, it will be noted will be understood that there are four such cyiin ders and that'suitable lateral connections are made from the various pipes shown in Figure 4- to assure the instantaneous admission of fluid to all of the clamping cylinders. This fluid, after filling upthe, spaces in the clamping cylinders, will cause the pistons II to move downwardly and permit a lowering of the gripping plate 88,

eventually causing the nuts l8 flrmly to clamp the plate 24 and its die strips 25 against the metal sheet ll. Y

When sufl'lcient pressure has been built up at I the rear of the pistons II, in the manner dethat the pump 21 is mounted directly on the fluid tank 3| so as to reduce the length of pipe necessary between the intake of the'pump and the tank. As in the case of Figure 2, there is a' fourway valve 33 employed, in which the high pressure ingress from the pumpis indicated at 34 and the low pressure egress at 88 and 88. The

scribed, the excess fluid from the pump, or rather which the admission valve 88 is set, all of the highpressure' discharge pipes are indicated at l 31 and 38. Similar elementsin this figure are given the same corresponding numbers as in Figure 2.

A pipe 80 is taken from the lower portion of the main piston cylinder, this pipe extending, upwardly as indicated at 8|, and then-horizontally at 82, passing through the admission valve 5to a position at the rear of theclamping piston i4. From the vertically extending pipe 8| there is a horizontalpipe 88, which connects with the clamping cylinder, at a position to the front of the clamping piston l8 and. at-a distance upwardly from the base 2. il'here is also a vertical pipe 88 connected through a check output from the pump will be passed through a t the valve to the working side of the main piscylinders becomes less than that 11 valve as at the top to, the pipe llataposition between the admission valve and the clamping cylinder. The lower end of pipe 84 is extended through a horizontal" length, indicated at 88, which connects with the high pressure discharge pipe .31. The other 7 38 connects through branch pipe lines 81 and 88 to the lowermost portion of the clamping cylinder l2v and to the rear 01' the main piston 5,

respectively; As shown on the drawings there is also a'short length of pipe 88 connected between I the two horizontal pipes 88 and 88 through a check valve 88.

the latter either 'moves .or

ton 5, causing the plunger 1 to be elevated. It

will be understood that ii for any reason thepressure in the upper portions of the clamping ecessary to operate the admission valve, fluid is admlttedto the clamping cylinders until the pressureha's been restored, tothe predetermined value, at which time the excess pressure fluid will be ivypassed through the valve into the main cylinder. the plunger 1 continues to rise-the punch 8 (Figure-'2) contacts with the metal sheet II and forms the sheet into an article of desired shape,

as was explainedin connection with Figure 2.

Upon completion ot'the operation, as may be either automatically determined or visuallyobserved by the operator, causes to be moved the rod 88 to the right,rwhich is the position high pressure discharge pipe ;The position of the main piston is shown as,

having completed its downward stroke, and the clamping pistons i4 ash'avi'ng been elevated to raise the gripping plate 24 to such a positionas to enable the previously formed article to be removed and a new sheet 01' metal ll placed in position-between the plates 88 and". Assuming that the pump 21 is delivering :high pressure fluid through the'pipe 82' and that it is desired to start the main piston I on its upward cylinder to the rear other portion into the sure is removed from the lower shown in Figure .4, Under these c the high pressure discharge or the pump is now admitted'to'the discharge nine 88 and a portion or the pressure fluid is introduced into the main or the piston l,- and the clamping cylinders below the pistons 14. It will be noted that the pipe 88, which communicates with the lower portion of the main cylinder, is the check valve 88 and the four-way valve 88 to the 10 wpressure pipe 88. 'Thus, all or the pres-- piston I, permitting the plunger descend. 'In order .to prevent an wardmoveme .1 readily to abrupt down-e to inserta choke valve (not shown) in the pipe working stroke, the rod 89 is moved to the left in any suitable manner, automatically or. mani ually through the use of levers, a motoror elec-" tro-magnet. Under these circumstances high 1 pressure fluid passes through the valve 88,

through the pipe 88 and the check valve,"- (noting that the vane of the check valve is pivoted to permit upward flow of fluid), into the space to the rear of the piston cylinders l4. H75- 88, which restricts the rate of flow of pressure fluid therethroughr High pressure mm travels through-the pipes 88 and '88 to the space at the rear of the main piston 8, forcing the carried thereby down- I wardly and thus breaking the mechanical con,-

tact between the punch and the under side oi the formed metal article. i

In view'otthe fact to descend rather space at the rear of most of the pressure that the plunger I tends the piston I at a rapid rate, fluid delivered'by the pump the path or the pipe 82, as in D ing or rorming I now connected through surface or the nt of the pistonfit' may be desirable quickly,; thus increasing" the on the shoulders of where within the hydraulic system during either fluid to the rear of thepistons I4 to be I ofthe metal during these pistons will elevate to .a height'determined by the position of the horizontal pipe 33, which in effect, causes the pressure fluid to be exhausted through the .line 99 and the valve 33, into the low pressure pipe 30. The clamping pistons I4 will therefore float or fluctuate between the .position of the pipe 33 and the lower end of the clamping cylinders.

When the pistons have reached this floating" position, the gripping plate 24, which is carried L the clamping plungers I9, will have reached its greatest distance removed from the plate 23 to enablethe formed article II to be maneuvered out from between the plates 23, 24. It isapparent that the width of the space between the plates 23, 24 can be made as great as desired, dependingon the shape of the formed article, by simply changing the position of the horizontal pipe 03 with respect to 25 the lower surfaces of the cylinders I2. After the formed article has been removed a new metal sheet can be readily inserted into position be cause the plunger I will have moved to its lower limit of travel, at which time the operator will cause the pistons 40, H to be moved to the left, thus applying first a clamping force to the plungers I Ii and then an upward movement of the main plunger I.

As in the case of Figure 2, there is preferably provided a pressure safety device I3 attached to the pump, the purpose of which is to shift the flow control ring in the pump to neutral when excess pressure has been developed anythe. upward or downward movements of the clamping plungers I9 or the pressing plunger I.

It will be evident that by assuring the main piston 5 would not be moved upwardly until a predetermined pressure has developed at the rear of the clamping cylinders I4, a clamping pressure is always applied to the plate 24 and therefore on the metal sheet I l before the punch 9 reaches the underside of the metal sheet. In view of the fact that theadmission valve 5 is essentially-a one-way element, the pressure built up at the rear of the clamping pistons will be maintained for an appreciable length of time after the plunger I :has started its-downward movement, thus assuring the proper amount of clamping pressure at the work when the punch 9 breaks mechanical contact (ii e. is stripped) with the under side of the formed article. This residual back pressure is relieved only when the clamping cylinders II are forced upwardly for go a considerable distance, causing some of the I passed through the admission valve 55 and through the horizontal pipe 33 to the opposite side of each piston I4.

It is further evident that the admission valve 55 may be so designed or regu ated as to provide any desired clamping pressure at the pistons I4 so as to permit the proper amount of slippage of the sheet II with respect to the plate 24 to accommodate the necessary stretch the forming operation. 'If desired, the clamping pressure may be made so high as to prevent any slippage whatever. In any case, equal pressures are applied to all of ceive pistons pipe H4 extending from V theyalve 33 to the clamping pistons, assuring equal clamping effects at the .plate 24 andthereiore a perfectly symmetrical formedarticle,

In Figures 5 and 6 there is shown still another embodiment of the present invention, the main diiierences being the manner in which the gripping plate moves with respect to the top plate, and also the. feature of maintaining. the pistons of the clamping cylinders practically stationary while moving the clamping cylinders yin respect to the pistons. The press is confined to a frame constituted. of a flat base member 92 of rectangular configuration, having countersunk holes 93 at the comers thereof for receiving the heads of a number of strain rods 94, threaded at each end. These rods are firmly secured to the base 92.by nuts 95, and their upper ends carry a top plate 96 secured in position by pairs of nuts 91. The top plate has a rectangular opening which is adapted to receive die strips 98, bolted or otherwisesecured thereto. The base member 92 'is provided with an upstanding cylinder 99 at the center, in which a I piston 5 and plunger I are adapted to reciprocate. The plunger I has a tumed-down shoulder I00 at the top, and this shoulder portion carries the usual platen 8 and the punch 9.

Surrounding the shouldered portion and rigidly secured thereto there is a hub vI0I, from which radiate, at equi-distant positions, four wing-shaped members I02 which take the general form of an S-coniiguration, and are constituted of flat pieces of metal terminating in a number of cylinders 'I03. These cylinders are bored, as indicated at I04, from the top and closed at the bottom. The bores I04 slidably regular gripping plate I06. Nuts I01 may be employed to assure rigid contact between the plungers-and the plate. The plate I06 has a rectangular opening similar to the top plate 93, and the sides of the opening are adapted to detachably receive die strips I08 which-may be secured as by bolts thereto. These die strips are provided not only'with inwardly projecting die surfaces, as'in the case of the other embodiments, but also with an additional lip I09. These lips I09 contain openings which-receive guide rods IIO which are firmly secured to the lips by nuts III. The lower ends of .the rods IIO move through openings which are provided in extensions I I2 formed on the wins members I02. The rods at the bottom may carry nuts I I3. The arrangement is such that the wins members I02 are adaptedto slide upwardly over the rods IIO, the nuts II3 assisting in determining the lower limit of travel of the wing elements. The hydraulic system includes the pump 21, the oiltank 3|, the four-way valve 33 and the high pressure line 32 andthelow pressure line 30, as in the previous embodiments. There is a the upper surface of the lower end of the cylinder 99. A length of pipe 5 connects the space to the rear of the piston 5 with the upper surface of the valve. There is a fluid inlet opening H6 at into a rectan the lowermost portion of each clamping cylinder I03, and this openin is connected to the highpressure side of the pump through a flexible pipe I" and a check valve H8. It will be noted that this valve is so arranged as to permit fluid to pass inwardly toward the bore I04 of the clamping cylinders. It will be understood that communication is made between the high pressure side of the pump and I05, which are threaded at the top the lower portions cylinder in order to facilitate adjustment.

2,2 9,584 of all of the clamping cylinders through their j respective check valves 1 II. A. flexible pipe I I9 is taken from the low pressure side of the-pump or the oil tank 3|, through an adjustable pressure relief valve I20 and a short length of pipe III, to the opening H0. This valve may be conveniently secured to the upper portion of the As in thecase of the previous embodiments. there is a choke valve I22 positioned in the low pressure line 36 leading from the valve 33.

The parts in Figures 5 and 6 are shown at the instant that the main piston 5 has reached its lower limit of travel, and it is assumed that the finished article formed by the previous pressing operation has been removed .irom the machine A fresh metal sheet II is placed in position withpressure of the fluid inthe bores 'I0l. However, it will be noted that these'bores are always in communication with the high pressure side of the pump through the flexible. pipes III, and further that the only way the fluid can escape is through the relief valves Illiv which are set/to, op-

' erate only above a predetermined pressure. :Con-

in the space between the die strips 25 and I00.

The operator then causes the rod 38 of the four- I way valve tobe moved to .the left, causing high pressure fluid to be introduced into the pipe Ill. As the pressure below the main piston increases, the plunger 1 will rise and will carry the wing sequently, while the pressure is reduced to some extent by the movement downwardly of the cylinders I03, nevertheless there is suflicient, pressure still exercised on the plungers I05 to v maintain suflicient clamping effect between the plates 00 and I00 when the punch 9 breaks contact with the formed metal article. As the plunger I continues its downwardlmovementj the cylinders I03, tra vel' downwardly a ,corre sponding distance, which eventually will reduce the pressure of the contained'fluid to such a value as to permit the plate- I08 to. descend of its own weight. Such a condition is under the direct control of the adjustments accorded the members I02 upwardly together with the clamping cylinders I03. These cylinders have been previously filled with fluid through the conduit I I! andthe check valves IIO. Consequently, as the cylinders move with respect to the plungers I05 the'fluid within the bores I04 is immediately placed under pressure, causing the plungers to move upwardly and to-press the gripping-plate I06 against the work II, thus holding the metal sheet firmly between the plates 90 and I06. Continued upward movement of the plunger causes the plungers I05 to be pressed upwardly'with greate force, thereby increasing the clamping effect at the metal sheet. 1

In the event that this pressure becomes exces- S1Ve, surplus fluid the bores I. is permitted to pass from the'inlets Ill into the vertical pipes I2I where they operate the relief valves I20, and this fluid is then permitted to return to the tank through the "conduits Ill. The clamping eflect at the plates I00 and "is entirely completed at the time the plunger 1 is moved to such a height as to cause the punch 0 to contact with the metal sheet. 0 Continued movement of the punch will cause the required deformation of the metal sheet, in accordance with the shape and size of v the opening between the upper die strips 25 and as alsodetermined by the shape of the punch. It'is apparent that during the upward movement of the plunger the wings I02 slide upwardly over the guide rods III. The fluid which is entrapped at therear side of the piston 5 finds ready access to the low pressure side of the pump or a tank through the pipes I II and 30. When the punch has reached its upper limit of travel, as deter mined' by the operator or in any other suitable manner, the rod 00 is movemto the right, which is the position shown in Figure 6. Under these conditions high pressure fluid 'passes from the pipe 32 to the pipe III which leads to the rea'." side of the piston I. At the same time thespaca 'in front of the piston is the tank through the pipes Ill, 38; the choki;

I valve I22 and thepipe 30. The choke valve I22 is for the purpose 'of limiting the rate at which ythe-fiuid is exhau'stedirom the front side of the main piston duringthe downward movement oi that pistom I As the plun er I moves. downwardly, due to l the pressure fl id passing through the pipe H5, it c arries with it the punch 9 and the wings I02., 0 The cylinders I" carried. by the wings also in communication with 6 main cylinder and the working pressure space relief valves I20, and preferably takes place only after the punch 0 has moved anappreciable dis-v tance away from the work.

Thus'it is evident that clamping pressure is assured at a time prior to when contacts the metal sheet during stroke and is also maintained for a sufilcient the punch 9 .length of time after the punch starts to descend.

It is further apparent that the time relation between. these clamping effects andthe move-, 1

ment of the punch can be accurately correlated and adjusted by proper control 'of the pressure, relief valves I20. The adjustment of these valves also affects the intensity of the clamping force so that any degree ofgripping action may be obtained in order to permit slippage between the metal sheet and the clamping plates, or

firmly to hold the sheet without any slippage whatsoever. It is further. .evident' that by the use ofthe individual relief valves, I20 for each clamping cylinder, any specialand local clamping effect'can be obtained, for example, by adjustin'g one or more of these valves to be'actumaining valves.

ated ata-diilerent'relief pressure than the re- It will be understood that we desire to com-- prehend within our invention such modifications as come within the scope of the claims and the invention. I I

Having thus fully described our invention, what we claim as new and desire to secure by .Letters Patent, is: l k

l. A hydraulic press comprising main and work-clamping cylinders,

pistons in saidcylin ders, a punchcarriedby'the piston in the main cylinder and a clamping plate carried by the tween, the punch and the metal sheet until the piston in the clamping cylinder and the clamping plate carried thereby have-moved into clamping position, said-means including a direct'fluidconnectionibetween the back pressure space of the of the clamping cylinders.

-- 2. A hydraulic press comprising i a pair of parallelly disposed platesadapted to receive and move downwardly, which tends to reduce the.

the working i clamp the edges of a metal sheet therebetween, said plates having openings in alignment, a cylinder under .the aligned openings and containing a piston, a punch carried by the piston of said openings, a source-of pressure fluid for operating said piston, and means including fluid obtained directly from the back pressure space I of said' -cylinder for applying clamping pressure to said-plates.

3. A hydraulic press comprising a pair of parallelly disposed plates adapted to receive and clamp the edges of a metal sheet therebetween, said plates having openings in alignment, a main cylinder in line with 'said openings and containing a piston, a punch carried by said piston and adapted to press the unclamped por tion of the metal sheet through said openings to form an article, a plurality of auxiliary cylinders symmetrically disposed about said plates and on the same side of the metal sheet as the main cylinder, said auxiliary cylinders containing plungers secured --at one end to one of the clamping plates and at the. other end to pistons which reciprocate in the auxiliary cylinders, the plungers in the auxiliary cylinders being adapted to move only in a direction opposite the direction in which the piston in the main cylinder moves, and means including a source of hy- .draulic energy .for. forcing the main piston in the direction of said metal sheet for forming the article, said means also serving to move the pistons in the auxiliary cylinders away from the sheet to cause said plates to grip the sheet during the forming operation.

4. A hydraulic press comprising a pair of parallellydisposed plates adapted to receive and clamp the edges of a metal sheet therebetween, said plates having openings in alignment, a main cylinder in line with said openings and containing a piston, a punch carried by said pistonland adapted to press the unclamped portion of the metal sheet through said openings to form an'article, a plurality of auxiliary cylinders symmetrically disposed about saidv plates and on the same side of the metal sheet as the main cylinder, said auxiliary cylinders containing plungers secured atone end to one of the clamping plates and at the other end to pistons which reciprocate in the auxiliary cylinders, the-plungers in the auxiliary cylinders being adapted to move only in a direction opposite thedirection in. which the piston in the main cylinder moves, means including a source of hydraulic energy for forcing the main piston in the direction of said metal sheet for forming the article, said means also serving to move the pistons in the auxiliary cylinders away from g the sheet to cause said plates to grip the sheet during the forming operation, and means for reversing the movement of the pistons in the main and auxiliary cylinders to cause the punch j to'leavethe formed article and thereafter to cause the clamping plates to be moved with respect to one another to permit the formed article to be removed from the press.

5. A hydraulic press comprising main and auxiliary cylinders, said cylinders containin pressure fluid, the auxiliary piston being secured to a plate which serves to clamp a metal sheet to the press, the main cylinder piston carrying a punch which serves to press the metal sheet into an article of predetermined shape, the pistons in said auxiliary cylinders being adapted to move only in a direction opposite the direction in which the piston in the main cylinder moves, means for applying the fluid to saidcylinders such that the metal sheet is clamped against the press before the punch contacts with the sheet, and means for reversing the stroke of all of said pistons whereby the punch is retracted from the formed article and thereafter the article is released from the press.

6. A hydraulic press comprising main and work-clamping cylinders, pistons in said cylinders, means including fluid conduits between said cylinders for causing the actuation of the piston in the wor -'clamping cylinder when the back pressure on the piston in the main cylinder reaches a predetermined value, and means for maintaining working pressure in the clamping cylinders for a definite amount of time after the back pressure in the main cylinder has been relieved.

7. A hydraulic press comprising main and work-clamping cylinders,,piston s. in said cylinders, means including fluid conduits between said cylinders for causing the'actuation of the piston in the'work-clamping cylinder when the back pressure on the piston in the main cylinder reaches a predetermined value, means for maintaining working pressure in the clamping cylinders for a definite amount of time after the back pressure in the main-cylinder has been relieved,

plate carried by the clamping piston for holding the sheet in position during the forming process, a source of pressure fluid and a cotrol valve therefor, said valve being provided with high pressure and low pressure openings which communicate with said source, a piston in said valve,

said valve also being'provided with a pair of openings A, B which are adapted to be an ingress and egress respectively for the fluid in an alternate manner dependent on the position of the piston within said valve, a conduit extending from opening A to the working side or the main piston, a conduit C extending from opening B to the rear side of the clamping piston, a conduit D extending between the rear side of the -main piston to the working side of the clamping piston, a conduit E extending between the working side of the clamping piston and the conduit C, a conduit F extending from the clamping a cylinder to the low pressure side of. the source offluid, and means positioned in the conduit E for assuring a predetermined pressure of the fluidon the working side of the clamping pistons before the pressure of the fluid in the main cylinder is suflicient to cause the punch to contact the metal sheet.

9. A hydraulic press comprising a main pressing cylinder and an auxiliary clamping cylinder,

pistons all actuated by a' common source'of a piston in each of said cylinders, a punch carried by the main piston for forming a metal sheet into a desired shape, a clamping plate sheet in position during the forming process,

, a. source of pressure fluid and a control valve therefor, said valve being provided with high pressure and low pressure openings which com-r municate with said source, a piston in said valve, said valve also being provided with a pair of openings A, B which are adapted to be an ingress and egress respectively for the fluid in an alternate manner dependent on the position oi. the piston within said valve, a conduit extending from opening A to the working side of the main piston, a conduit C extending from opening 13 to the rear side of the clamping piston, a conduit D extending between the rear side of the main piston to the working side of the clamping piston, a conduit E extending between the working side of the clamping piston and the conduit C, a conduit F extending from the clamping cylinder to the low pressure side of the source of fluid, and means positioned in the conduitE torassuring a predetermined pressure of the fluid on the working side of the clamping pistons before the pressure .of the fluid in the main cylinder is sumcient to cause the punch to contact the metal sheet, said means comprising an admission valve adjusted to open the passageway through conduit E when the working pressure on the clamping piston has reached a pre- 

